The mystery of a lost Rene Magritte canvas missing for nearly 80 years has been solved by conservators and curators at New York's Museum of Modern Art amid preparation for an upcoming exhibition.

While the painting did not end up in an oven, as is feared of some other 20th-century masterworks, it was destroyed—in this case by the "Ceci n'est pas une pipe" painter himself, who recycled the canvas as the support for other, smaller works. Curator Anne Umland and conservator Michael Duffy described their unexpected findings, and their hopes for future discoveries, in a recent conference call with A.i.A.

The 1935 painting that started it all, The Portrait, is part of MoMA's collection and is slated to appear in "Magritte: The Mystery of the Ordinary, 1926-1938" (Sept. 28, 2013-Jan. 12, 2014). The first exhibition to focus on his Surrealist years, it's also the first full-scale U.S. show since the Metropolitan Museum's "Magritte" exhibition in 1992, and will feature over 80 works.

The canvas, not quite 29 inches high, shows a tabletop still life with an eye peering out of a thin slice of what looks like prosciutto—a characteristic motif for the Belgian Surrealist (1898-1967). While inspecting the painting in fall 2011, Duffy and his colleagues noted their first clue that there was something unusual about this work: the canvas was painted on the edges. Usually, Duffy said, Magritte's paintings' sides show only white primer.

The customary inspection of a painting's condition also involves X-rays, Umland said. "Funny enough, just after we took the X-ray, the painting went out on loan," Duffy said. "Then we developed the X-ray and saw that there was a visible figure underneath—though, since the underlying image is perpendicular to the imagery of The Portrait, it took us a while to figure out what it was."

The X-ray revealed the head and torso of a female nude. Since other canvases by the artist had revealed overpainting, Umland told A.i.A., this came as a surprise but not as a shock. The next task was to identify the earlier, obscured painting. This happened quickly in a conversation with conservator Brad Epley, at Houston's Menil Collection, which, along with the Art Institute of Chicago, is co-organizing the exhibition with MoMA.

"When Brad saw the X-ray," Duffy said, "he noted a similarity to a painting in the catalogue raisonne, The Enchanted Pose, from 1927. Its whereabouts, according to the catalogue, were unknown." That painting showed two identical female nudes, side by side, each resting an arm on a broken column. But the nudes were full-length, not the partial figure revealed by X-rays of The Portrait.

The Enchanted Pose wasn't just any painting, either, the conservator added: "It was critically acclaimed when it was shown in a 1927 exhibition at Le Centaure. However, further down the line, there was also a 1932 letter from the Palais des Beaux-Arts in Brussels, instructing Magritte to come and retrieve the painting, which had been languishing there."

How did a successful painting come to be so neglected? The curator and conservator can only speculate, they admit.

"He's at a very different place in his career in 1935 from 1927," Umland pointed out. "One can hypothesize that he had moved on. Was The Enchanted Pose too Picasso-like? Was he no longer interested in strategies of doubling? Or perhaps the condition of the painting had been compromised."

"Or it didn't sell," Duffy said, "and at some point he needed the materials."

"But it wasn't a moment of particular financial distress for him, as far as I know," Umland countered.

Assuming that the painting was cut into quarters and that Magritte used all four smaller canvases during 1935, the curator's and conservator's next step was to identify paintings of the same date and size as The Portrait, of which there are several, and contact the owners. Did the canvases have paint on their sides? This would be the first step in the process of elimination.

"The next painting on our list," Umland said, "turned out to be an instant hit!" The Red Model (1935), from Stockholm's Moderna Museet, also revealed underpainting when X-rayed. Its image, of a pair of disembodied feet that transform, on the way from toes to ankles, into boots, concealed the bottom left quadrant of The Enchanted Pose.

So now half the destroyed painting has been located. Where are the remaining two quarters? Duffy and Umland have identified what seemed like four strong candidates, but they crossed two off the list after inspecting them—no paint on the sides.

"There are several canvases that we haven't had a chance to inspect because they are in private hands," Umland said. "To x-ray and examine a work in a way sufficient to answer our questions is a bit of a project. And there are some that might fit the bill but whose location we don't know."

The dismemberment of a painting, while it might dismay an art historian, bears a certain resonance with some of Magritte's practices, the curator and conservator pointed out. They cited several works from 1930 that the artist called "painting-objects," which consist of several separate canvases that constitute a single work.

"And there are multiple works from the period we're looking at in which he divides his pictures into quadrants," Umland pointed out, citing Man Reading a Newspaper (1928), from the Tate, in which the image is divided into four comic book-like frames. "And he often does images of the backs of paintings that are divided into quadrants by stretcher bars," Umland said, "so this idea of quartering, dividing, gridding, cutting, all as a way of countering seamlessness, is there in his practice."

As for the possibility of finding two canvases that would fill out The Enchanted Pose, said Umland, "We remain hopeful. Once the exhibition opens we're in a new phase, because many people will be coming through our doors, and we can ask them, ‘Do you happen to know . . . '"